The present invention relates to a control apparatus for controlling plural power loads in a vehicle and in particular to an apparatus with over-current and over-temperature shutdown means that are safe and inexpensive, and that effectively protect an integrated circuit in which an abnormality over-current can flow in response to a load short-circuit etc.
According to a technique which is commonly employed in conventional systems, the current supplied to a load is detected, and when the current becomes too large, it is shut down automatically. This system has been used, for example, in connection with MOSFET (Metal Oxide Semiconductor Field Effect Transistor), as disclosed in, for example, Japanese application patent laid-open publication No. Sho 61261920, Japanese application patent laid-open publication No. Sho 62-11916, Japanese application patent laid-open publication No. Sho 62-143450, and Japanese application patent laid-open publication No. Sho 63-87128, etc.
However, these current detection systems become problematic on occasion. For example, where the load is a head lamp etc. in an automobile, switching from an off condition to a light-on condition, elimination of a momentary large current interferes with smooth lighting of the lamp. That is, it results in a noticeable delay until the light comes on under a necessary timing and the lighting is thus obstructed. In other words, it is necessary and indispensable to have an abrupt current during this regular use condition.
For this reason, in a technique shown in Japanese patent application No. Hei 8-303018, monitoring the temperature but not current permits a short-circuit of the load and a momentary current at the regular load, and further during an abnormality short-circuit accident and an operation in which it is shut down automatically.
However the above described technique presents a further problem which is unavoidable when plural loads are controlled by a single chip integrated circuit. In the case of the employment of an over-current abnormality detection system, each over-current abnormality automatically shuts down the circuit, which does not reset automatically. Thus, this system is vulnerable to a malfunction caused by noises. That is, when a large current surge momentarily and suddenly shuts down the system, and the system is not reset, the convenience of the system is diminished.
After switching from the abnormal condition to the shutdown condition, and the abnormality detection current is lowered, the system returns to the continuity condition. In this case the current can be limited to some degree. However, when the load short-circuit is generated repeatedly, semi-continuity is continued, and a rise in temperature and deterioration of the element are likely.
Further, the system for detecting over-temperature cannot specify which element on the same chip is causing the heat generation and the abnormal temperature. Further, when scattering in the circuit for realizing the temperature detection is not neglected, and when an improvement of accuracy is devised, such an apparatus must be a very high cost apparatus.
As stated above, in the power element having only a single protection function according to the temperature or the current, it is impossible to control the system to shut down automatically and to return suitably by sensing an abnormality in the element which controls the continuity and shutdown of the current to the plural loads. Further, in a shutdown method for detecting an abnormality of the current or of the temperature in each individual load, the circuit construction becomes complicated and expensive.
An object of the present invention is to provide an apparatus with an over-current shutdown device and an over-temperature shutdown device wherein by compatibly combining a current protection function of a power element at a continuity condition with an over-temperature protection function (which has a slower reaction than that of the current protection function but can detect surely the abnormality), the abnormal power element can be specified.
Another object of the present invention is to provide an apparatus with an over-current shutdown device and an over-temperature shutdown device wherein, by compatibly forming a current protection function of a power element at a continuity condition, with an over-temperature protection function (which has a slower reaction than that of the current protection function but can detect surely the abnormality), a simple circuit construction can be realized with a low cost.
These and other objects and advantages are achieved by the control apparatus according to the present invention, which includes means for detecting a current abnormality of a power element, means for monitoring a temperature abnormality of a local area of the power element, and means for continuing or shutting down the power element based on information concerning the above stated current and/or temperature abnormalities with a timing which is established according to a substantially constant period or a time interval which is stored in advance in a memory element etc.